Thinking out loud

So, I woke up this morning in utter dismay. Humans seem to be naturally selfish, exploiting the kindness of a few selfless ones whenever they spot an opportunity. They strike before the kindhearted even realize what’s happening. My question is: if we’ve been like this for so long, how haven’t we driven ourselves to extinction? It’s hard to believe how the minds of the majority work. I’m seriously vexed.